BEIRUT — Syrian rebels today captured a crossing point along a cease-fire line in the contested Golan Heights patrolled by U.N. troops, an Austrian defense ministry official said.

The development is likely to deepen Israel's concerns that the volatile area in the north along the Israel-Syria frontier could fall into the hands of radical Islamic factions fighting along with other insurgent groups in Syria against President Bashar Assad's forces.

The crossing's seizure comes a day after the Syrian military, backed by Lebanese Hezbollah militants, captured the strategic town of Qusair near the border with Lebanon in a significant blow to the opposition fighters trying to topple Assad's regime.

The crossing in the Quneitra area, which is patrolled by Austrian U.N. peacekeepers, was overrun and seized by the rebels early today, said Col. Michael Bauer of the Austrian defense ministry.

Bauer told The Associated Press in Vienna that the Austrian peacekeepers pulled back from the crossing earlier and were unharmed. The ministry's crisis committee was meeting to evaluate the situation, he said.

The Austrian contingent is part of a U.N. peacekeeping force that patrols the Golan, captured by Israel in the 1967 war. The Quneitra is the only crossing along the ceasefire line and primarily serves the U.N. peace keepers and Druse villagers moving between the Israeli- and Syrian-controlled Golan.

The Britain-based activist group the Syrian Observatory for Human Rights said the rebels attacked Syrian regime checkpoints and their armored vehicles, and took control of the crossing, located near the old city of Quneitra.

The activist group, which relies on a network on informants inside Syria, said there were intense clashes underway between regime forces and rebels in the area today, and Assad's troops were shelling villages around the city. There were no immediate reports of casualties.

From the Israeli side of the Golan, tanks and armored vehicles could be seen from about a kilometer (half mile) away in the Syrian-controlled part of the territory. Thick smoke and flames rose from the area and a large fire raged.

Syrian state-owned Al-Ikhbariyah TV denied today that the rebels control the Quneitra crossing. The TV reported that the Syrian army was pursuing "terrorists" in the Golan, a term the government uses for opposition fighters.

Israeli Army Radio said the Syrian side of the Golan crossing had fallen into rebel hands. The Israeli military would not confirm the report, but said the Israeli side of the crossing has been declared a "closed military zone" and was off limits to journalists because of the fighting nearby.

The Syrian conflict started in March 2011 as peaceful protests against Assad's regime. It turned into a civil war after some opposition supporters took up arms to fight a harsh government crackdown on dissent.

The fighting is increasingly spilling over Syria's borders into neighboring countries, including into Lebanon where factions that support opposing sides in Syrian civil war have frequently clashed in the past year.

Islamic groups such as the al-Qaida-linked Jabhat al-Nusra have become the most organized and most effective force on the opposition side. The Nusra

There have been previous incidents in the Golan, with gunfire and mortar shells striking the Israel-controlled zone in recent months. Israel believes that most of the fire has been an incidental spillover from the Syrian conflict, but in some cases it said strikes were deliberate.

In one such incident last month, Syrian troops targeted an Israeli jeep on an overnight patrol that they said had crossed the cease-fire line into the Syria-controlled sector and was heading toward a Syrian village with a large rebel presence.

Syria said it launched two missiles in self-defense and accused Israel of violating the U.N. Charter and the separation of forces agreement that followed the 1973 Arab-Israeli war. After the 1967 capture of the strategic plateu, Israel later annexed the Golan Heights. Syria wants the territory back.

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Associated Press writers George Jahn in Vienna and Aaron Heller in Jerusalem contributed to this report.